Mercury SportJet 175 hp Excessive Oil Injection

[Grumman581]

I posted this to the wrong forum earlier, so here it goes again...<br /><br />I have a Mercury SportJet (175 hp) in a 1998 Sugar Sand Mirage. After the engine has been stopped for awhile, restarting it requires use of starter fluid. Once it restarts, there is quite a bit of smoking from oil being burned off. When I examined the plugs before starting the engine, they appear to have a lot of oil on them. Once the engine is running, the oil burns off after awhile and it runs normally. To say the least, this does not give me much confidence in the engine since it doesn't immediately start with the starter fluid due to all the oil in the engine and to say the least, it is not that fun to paddle it (been there, done that, got the t-shirt).

 

[B_Eager]

Re: Mercury SportJet 175 hp Excessive Oil Injection

Does it start properly cold? You may have a proplem with the chock not the oil mixture.

 

[Grumman581]

Re: Mercury SportJet 175 hp Excessive Oil Injection

The problem with a cold start is that by the time the engine is cold, enough oil has drained into the cylinders that it is quite difficult to start, thus the need for the starting fluid being sprayed into the air intake... Once I've burned off that oil, it will restart immediately without a problem, but if I leave it shutdown, it gets progressively more difficult to start... This is probably because oil is continuing to drain / be injected into the cylinders... From the rec.boats newsgroup, someone has mentioned that the header tank will gravity flow into the engine during various problems even with the engine off... I don't have the boat at my house right now, so I can't check look at it... I'm hoping to get some idea from various people so that when I bring the boat home in a few days, I'll have a list of things that I need to check...

 

[B_Eager]

Re: Mercury SportJet 175 hp Excessive Oil Injection

I am confused, 1998 175 Mercury Jets are not fuel injected. They are oil mixed before the carberator. If what you are saying was true you would have a horrible time getting it started after being parked for a week,true?? Have tried pinching off the fuel line to the choke, and trying to start the boat.

 

[hondon]

Re: Mercury SportJet 175 hp Excessive Oil Injection

Here,s what happens.Your oil injection mixes oil and fuel before the carbs and sends that mix to the float bowls.During layup the fuel in the bowls evaporates but the oil do'es not.It does'nt take long for this to happen.Using quality oil makes a big difference.

 

[wakataka]

Re: Mercury SportJet 175 hp Excessive Oil Injection

Same problem - Different engine. <br />I've got a SportJet 90 that is addicted to starting fluid for the first start of the day. After that, it will start fine even after sitting for a couple of hours. Plugs are wet when removed during attempted cold starts. Choke is working. It only needs a small whiff of either to get it going then it runs fine. I premix my fuel so it can't be related to oil injection. My ignition system throws spark across a 3/8 inch gap, so I don't think it is weak spark. It's got me beat. <br /><br />Although the 175 and 90 hp sportjets have little in common, maybe we have the same problem here. If so, it's not related to your oil injection but I would sure like to know what causes it.

 

[Grumman581]

Re: Mercury SportJet 175 hp Excessive Oil Injection

Wave Dancer -- Sorry about the confusion of carburation vs fuel injection... I wasn't sure which one it was, so I was somewhat ambigous in my terminology... Yes, I have a difficult time getting it started after it has been parked for a week... I also have a difficult time after it has been parked for an hour... I haven't tried pinching off the fuel line to choke... Don't know if that would work since there is so much oil in the cylinders that it would take diesel compression to be able to burn it... <br /><br />hondon -- If the fuel is evaporating in the carb, I do not believe that there would not be as much oil being put in the cylinders as I'm seeing... When I pull the plugs, it is as if I had dipped them directly into 2-cycle oil... There doesn't appear to be any fuel dilution at all...<br /><br />RowHome -- I just wish mine only needed a 'whiff' of starting fluid... It takes quite a bit to get it started and it a couple of attempts each time... Well, I could probably do it on one attempt if I had another person helping by starting the engine while I'm spraying the starting fluid... The engine will start running and sputtering, but once it runs out of starting fluid, it quits... I can't get back into the engine compartment quick enough to add more starting fluid before it dies, so I have to go through this process a few times before it has burnt off all the oil that was flooding the cylinders...

 

[B_Eager]

Re: Mercury SportJet 175 hp Excessive Oil Injection

The 1999 model year was the first year to use an electric fuel pump. Have you guys tried a primer pump to get the fuel up to the carburater. I think you guys with the cold start problem could be dealing with a vapor lock. I used to deal with that with my old Welcraft I/O, starter fluid to get it started till the engine could pump it's own fuel up. As for the oil flooded condition, If you are that oil loaded, are you sure that the auto oil mixer is not bad, maybe a bad O-ring?

 

[clanton]

Re: Mercury SportJet 175 hp Excessive Oil Injection

I would look at the anti-siphon valve, the all aluninum valves are junk, use a the OMC valve which is a brass valve with stainless steel insert and ball. There are check valves in this system, and they gum up just like the carbs. Im not sure about the primer pumps for the Mercs, but the hard starting is from lack of fuel. One thing you could use for a primer is a Walbro electric primer pump, to prime the carbs. Could just need carbs cleaned.

 

[Grumman581]

Re: Mercury SportJet 175 hp Excessive Oil Injection

Well, I've got some new information on my testing of my engine... Perhaps this will make sense to someone...<br /><br />I brought the boat home the other day so that I could do some testing on it... As expected, it was rather difficult to start... The battery being somewhat low didn't help matters much, but with a little starting fluid sprayed into it beforehand, it fired... After a couple of times of this, it ran long enough for me to get to the engine compartment so that I could give it a burst of starting fluid every few seconds to keep it running... After a minute of this, it was able to run on it's own with me just advancing the throttle a little bit.. I looked at the engine installation, but I could not find any sort of check valves in there... I don't doubt that they are there, but the engine compartment is somewhat crammed and I probably don't really know what I'm looking for... <br /><br />I checked the cover on the oil reservoir over the engine and it was tight... I checked the caps on the external oil reservoir and they were tight also... I noticed a placard that said that if the caps were loose, it could result in insufficient oil going to the engine... This got me to thinking, so I loosened the cap on the reservoir and noticed air pressure was being kept in there so I suspect that one of the hoses that runs to it is to pressurize the reservoir to use that to pump the oil into the main reservoir over the engine... After I shut down the engine, I noticed that there was still pressure in the reservoir... Is this normal? If this reservoir is under pressure even when the engine is off, could it perhaps cause it to flood the engine with oil? I tried to start up the engine soon after having shut it down and it did not have a problem... I then again released the pressure in the external oil reservoir... I came back to it today and attempted to start it again without using starting fluid... Normally a wait of a day would result in me having to use starting fluid to start it and there being a lot of smoke being produced as the engine burnt off the excess oil that was in the cylinders... That was definitely not the case this time... So, I have a way around the problem, but I don't know exactly what the problem is really caused by... Anyone have any ideas?<br />

 

[clanton]

Re: Mercury SportJet 175 hp Excessive Oil Injection

Check valves.

 

[B_Eager]

Re: Mercury SportJet 175 hp Excessive Oil Injection

If I understand how the 175 oil inject system works. You have a main oil tank that pumps into the small tank up by the engine. The check valve I would think would be somewhere in the upper tank, (try the cap), could be that simple.

 

[clanton]

Re: Mercury SportJet 175 hp Excessive Oil Injection

If you follow the oil line from small oil tank on engine to oil pump, then from oil pump to fuel line, the check valve is located in the oil line at the T that connects the oil line to the fuel line. May differ on EFI engine. Check oil pump adjustment. Remove oil line from outlet side of pump, should not be lot of oil bypassing pump. There are other check valves and vents in system, you need diagram of system for a complete check of all valve and vents, plus pump adjustment.